The present invention relates to a map display device and a map display method for displaying various maps such as a road map or the like, a navigation device to which the map display device is applied, and an automobile equipped with the navigation device.
Various types of navigation devices to be mounted on an automobile or the like are developed. The navigation device comprises a large capacity data storage means such as a CD ROM or the like in which, for example, road map data are stored, a detecting means for detecting the present position, and a display device for displaying the road map of the place near the detected present position on the basis of the data read out from the data storage means. In this case, as the detecting means for detecting the present position, there are a means using a global positioning system (hereafter referred to simply as a GPS) utilizing an artificial satellite for positioning, which is called a GPS (Global Positioning System), a means by the autonomic navigation in which the change of the present position is traced from the start point on the basis of the information such as the running direction of the vehicle or the running speed, and the like.
Then, the data of the road map of the place near the present position detected by the detecting means for detecting the present position, are read out from the large capacity data storage means such as a CD ROM or the like, and a picture signal for displaying the road map is prepared, and the picture signal is supplied to a display device, and the road map of the place near the present position is displayed thereon. There is a case where the main body of the navigation device and the display device are composed of separated bodies, too. Moreover, it is also possible to display the road map of a desired position or the like at home or the like without mounting the devices on a movable body such as an automobile or the like.
By the way, in such a navigation device, it is also possible to display a map of an arbitrary position besides a map of the measured present position by operating a control key or the like, as long as the map data are prepared by a CD ROM or the like. For example, it is possible that from the state where the road map of the place near the present position is displayed, the displayed map is scrolled in an arbitrary direction by operating a cursor key or the like so that a map of an adjacent position may be displayed.
Such a scroll of the display range of a map is a scroll in which for example, by continuously pressing a cursor key corresponding to the direction of scrolling, the display range is continuously changed in the corresponding direction while the key is continuously pressed, and in the prior art, the scroll speed during the pressing of the key is set to be constant. That is, for example, as shown in FIG. 1, the display range was changed in order at a scroll speed Va constant at all times from the start of the pressing of the key. The horizontal axis in FIG. 1 indicates the elapsed time since the start of the pressing of the key.
If the scroll speed is constant at all times like this, there is a disadvantage that for example, it takes a long time to display a map of a place far away from the present position. Therefore, a navigation device is developed, in which the scroll speed can be changed at a plurality of steps. That is, for example, as shown in FIG. 2, the scroll speed is set to be a comparatively slow scroll speed Vb until a predetermined time has been elapsed after the start of the pressing of the key, and when that time has been elapsed, it is set to be a fast scroll speed Vc, and further, when another predetermined time has been elapsed, it is set to be a faster scroll speed Vd. Thus, the scroll speed is changed at a plurality of steps, so that for example, if the key is pressed only for a short time, the display range of a map is changed at a slow scroll speed and it can be successfully performed to choose the map in the range adjacent to the range displayed at present, and if the key pressing time becomes long, the display range is scrolled at a high speed to a map in the range far away from the range displayed at present, and it can comparatively easily be performed to find a map of a distant place.
However, if the scroll speed is changed at a plurality of steps like this, there was a disadvantage that the state of map scrolling was suddenly changed at the point of changing of the scroll speed and when choosing a map of a place near the position of changing of the speed, the display of the map in the target range was overpassed and delicate operation was difficult.